I. Field of the Invention
The present invention relates to a process for synthesizing powders of titanium carbide, titanium nitride or titanium carbonitride by coating precursor particles thereof with carbon and heating the coated precursor particles to a temperature sufficient to produce a substantially complete solid solution.
II. Description of the Prior Art
High temperature carbides, nitrides and carbonitrides such as titanium carbide, titanium nitride and titanium carbonitride possess valuable characteristics including high strength, hardness, wear resistance, light weight, high temperature capacity and other properties that make them candidates for many applications. Some examples of use include cutting tools, bullet-proof vests, metal reinforcements, electronic resistors, and other products that can benefit from such properties.
Three present methods are known for the production of titanium carbide, titanium nitride and titanium carbonitride. The first method is a direct carbonization/nitridation of titanium metal or titanium hydride. This method requires five to 20 hours to complete, produces strongly agglomerated powders that require extensive milling to yield fine powders, and require a chemical purification to remove impurities from mill wear.
The second method is a gaseous pyrolysis of a titanium halide, such as TiCl.sub.4, in a nitrogen- or carbon-containing atmosphere. Generally poor yields are obtained, even at temperatures exceeding 1,300.degree. C., with reactions conducted at lower temperatures resulting in the formation of non-stoichiometric products. Because of this poor performance, no commercial processes employ this approach.
The third presently-known method for synthesizing titanium carbide, titanium nitride and titanium carbonitride is a carbothermal reduction of titanium dioxide with carbon in a controlled atmosphere (e.g. nitrogen or argon gas) at high temperatures (e.g. 1,700.degree.-2100.degree. C.). Reaction time is typically very long (10-20 hours), and powders produced generally have non-uniform particle sizes (therefore requiring subsequent milling) and undesirable inhomogeneities.
It is therefore apparent that a need is present for a process for producing carbides, nitrides and carbonitrides with uniformity, speed and economy. In accord therewith, a primary object of the present invention is to provide a process for synthesizing titanium carbide, nitride and carbonitride powders possessing high purity, narrow particle size distribution, and stoichiometry for use in making components and composites for structural and electronic applications. This and other objects of the present invention will become apparent throughout the description of the invention which now follows.